FR3077105A1 - FAN FOR AN AIRCRAFT COOLING UNIT - Google Patents

Abstract

A fan (16), in particular for an aircraft cooling unit, comprising a wheel (128) comprising a hub (138) and an annular array of blades (140), a drive shaft line (136) the wheel about an axis (A), and fusible connection means of the hub of the wheel to the shaft line, these fuse link means having a first mounting bushing traversed by the shaft line and surrounded by said hub, and safety fusible elements (174) which extend parallel to said axis (A) and are configured to break and disengage in rotation the wheel from the shaft line when a driving torque of the wheel transmitted by said shaft line exceeds a certain threshold, characterized in that said connecting means comprise a second wear sleeve (143) which is interposed between said first sleeve and said hub and which is traversed by said fuse elements, said second socket being realized e in a material different from that of the first bushing and susceptible to wear by friction and / or by heating in the case where the transmission line continue to rotate due to the above separation.

Description

FAN FOR AN AIRCRAFT COOLING GROUP

TECHNICAL AREA

The present invention relates in particular to a fan, in particular for an aircraft cooling unit.

STATE OF THE ART

The state of the art includes in particular document W0-A12017 / 046490.

Aircraft engines are equipped with fluid cooling groups such as oil for example. An oil cooling unit of the prior art comprises an air-oil exchanger and a fan which is intended to draw air through the exchanger.

The exchanger is generally of the “brick” type and the fan comprises a wheel which is arranged next to the exchanger and which sucks air through it so that the air takes up heat energy from the oil circulating in the exchanger.

The ventilator is a mechanical ventilator and its wheel is rotated by a shaft line which is connected to an output shaft of a gearbox or to mechanical levers on the engine of the aircraft.

Engine and / or helicopter manufacturers may require that, in the event of a problem with the fan wheel, such as a wheel lock or ingestion of a foreign object in the fan, the increase in torque driving the wheel beyond a certain threshold causes a controlled breakage of a part in order to decoupled or disengage in rotation the fan wheel from the output shaft of the gearbox or of the sampling means mechanical on the engine.

In the current technology, this safety function is provided on the drive shaft line of the fan wheel. The shaft line includes a section having a fusible portion intended to break in the event that the torque transmitted to the wheel exceeds a certain threshold. This section is then called "tree to break" since it is it which is intended to break in the aforementioned case.

In addition to this tree to break, the tree line includes several elements (main shaft, sleeve, bearings, flange, preloading washer, etc.) and is therefore relatively complex. The shaft to be broken forms an intermediate part which causes the wheel to offset from the output shaft and requires the shaft line to be guided by bearings and associated parts. Although this complexity is not required by the client, it is necessary to integrate the security function. The tree line is therefore expensive and has a large mass. In addition, the presence of the bearings decreases the reliability and the service life of the fan.

The Applicant has already proposed a solution to this problem in document W0-A1-2017 / 046490. This document describes a fan comprising the characteristics of the preamble of claim 1. It proposes in particular to provide the safety function on the fan wheel rather than on the drive shaft line of this wheel. The shaft line can thus be simplified and be less expensive and less heavy than that of the prior art. This reduces the cost of the fan but also increases its reliability. The fan wheel therefore incorporates a fuse element making it possible to decouple the wheel from the shaft line when the torque transmitted by the shaft or the shaft line exceeds a predetermined threshold.

In operation, the speed of rotation of the wheel can be very high and for example of the order of 10,000 to 20,000 revolutions / minute. After rupture of the fusible element, a very significant heating is created due to the relative displacements of the parts, which can cause their seizure or even their welding and thus result in a cancellation of the desired phenomenon of separation of these parts.

STATEMENT OF THE INVENTION

The present invention provides a simple, effective and economical solution to this problem.

The invention provides a fan, in particular for an aircraft cooling group, comprising:

a wheel comprising a hub and an annular row of blades, a line of drive shaft of the wheel about an axis, and

- Fuse link means of the wheel hub to the shaft line, these fuse link means comprising a first fixing bushing crossed by the shaft line and surrounded by said hub, and safety fuse elements which s extend parallel to said axis and are configured to rupture and disengage in rotation from the wheel of the shaft line when a drive torque of the wheel transmitted by said shaft line exceeds a certain threshold, characterized in that said connecting means comprise a second wear sleeve which is interposed between said first sleeve and said hub and which is crossed by said fusible elements, said second sleeve being made of a material different from that of the first sleeve and liable to wear by friction and / or by heating in the event that the shaft line continues to rotate following the abovementioned separation.

The invention thus proposes adding a wearing part to the fusible link means, this wearing part being configured to wear in priority in the case where the shaft line continues to rotate following a separation of the wheel of this tree line. The wearing part is an intermediate or intermediate part and therefore preferably avoids direct contact between the hub and the fixing sleeve, since it is this direct contact with generally metallic parts which generates the heating problem of the technique. earlier. The wear sleeve is advantageously configured to facilitate the sliding of the wheel hub with respect to the fixing sleeve.

The nominal torque to be transmitted by the fusible element of the wheel is preferably between 1 and 15 N.m. The breaking threshold can represent ten times the nominal torque, and be of the order of 10 to 150 N.m.

The ventilator according to the invention may include one or more of the following characteristics, taken in isolation from one another or in combination with each other:

- Said second bushing comprises a cylindrical portion and a radial portion, the cylindrical portion of the second bushing being interposed between cylindrical portions of the first bushing and of the hub, and the radial portion of the second bushing being interposed between radial portions of the first bushing and hub,

- said fusible elements are screws and ensure the fixing of the wheel,

the screws axially pass through the radial portions of the first and second bushings and of the hub,

the screws pass substantially axially through the axial orifices of the radial portions of the first and second bushings and of the hub,

- said first sleeve is held axially clamped against a shoulder of the shaft line by a nut screwed to one end of the shaft line,

said nut is supported axially on a washer which itself is supported axially on the cylindrical portion of the first bush, this washer being separated by an axial clearance from the cylindrical portions of the second bush and of the hub,

said first socket is made of metal and said second socket is made of plastic material.

The invention also relates to an aircraft cooling group, comprising a heat exchanger, for example air-oil, and a fan as described above.

The invention also relates to an engine or a gearbox for an aircraft, such as a helicopter, comprising an output shaft and a cooling unit as described above, the wheel of which is driven by said output shaft.

The present invention finally relates to an aircraft, comprising at least one cooling group or an engine or a gearbox as described above.

DESCRIPTION OF THE FIGURES

The invention will be better understood and other details, characteristics and advantages of the invention will appear more clearly on reading the following description given by way of non-limiting example and with reference to the accompanying drawings in which:

FIG. 1 is a schematic perspective view of an aircraft engine equipped with a cooling unit,

FIG. 2 is a schematic perspective view of the fan of the cooling group in FIG. 1,

FIG. 3 is a partial schematic view in axial section of the fan of FIG. 2, and represents the technique prior to the present invention,

FIG. 4 is a schematic view in axial section of a fan according to the invention, and

- Figure 5 is an enlarged view of part of Figure 4.

DETAILED DESCRIPTION

FIG. 1 shows an aircraft engine 10, in this case a helicopter, which is equipped with a group 12 for cooling the engine oil. The group 12 includes an air-oil heat exchanger 14 and a fan 16 which is better visible in FIG. 2.

The heat exchanger 14 is of the “brick” type and has a parallelepiped shape. It comprises an oil circuit connected to ports 18 for supplying and discharging oil, only one of which is visible in FIG. 1. It further comprises fins 20 defining heat exchange surfaces with a flow of air passing through the exchanger (arrow 22). The front or inlet section 24 of the exchanger has the shape of a parallelogram. The outlet section (not visible) of the exchanger is also of parallelogram shape. A connecting pipe is mounted between the outlet section of the exchanger and the suction or inlet section 26 of the fan and ensures fluid communication between these sections.

The fan 16 is here of the centrifugal type and comprises a wheel 28 which is driven by a shaft line 36 to force the air to be sucked through the exchanger 14 and to sweep the fins 20. The sucked air passes to through the wheel and is expelled radially outward. It is channeled by a pavilion 29 of the body 30 of the fan which forms a volute and extends from the aforementioned inlet 26 to the air outlet 32 which has a substantially tangential orientation (arrow 34) relative to a circumference centered on the axis of rotation of the wheel.

As seen in Figure 1, the exchanger 14 and the fan 16 are arranged next to each other. The fan body 30 is fixed on an engine casing and the exchanger 14 is generally fixed in overhang on the fan (or directly on the motor or the gearbox).

The wheel 28 of the fan 16 and the shaft line 36 for driving the wheel 28 are better visible in FIG. 3.

The wheel 28 comprises a hub 38 carrying an annular row of blades 40 at its periphery. It also comprises means for connection to the shaft line 36. These connection means 42 are housed in the hub 38 and are here formed in one piece with the latter. The connection means comprise a bore 43 passing through and extending along the axis A of rotation of the wheel. The blades 40 are also formed in one piece with the hub 38. The wheel 28 is thus in one piece.

The shaft line 36 comprises several elements: a main shaft 44, a second shaft or section of shaft called a “tree to be broken” 46, bearings 48, a sheath 50, and additional parts such as a flange, a preloading washer, hardware, etc.

The main shaft 44 has one end which passes through the bore and comprises rotational coupling means which cooperate with the connection means 42 of the wheel 28.

The opposite end of the main shaft 44 receives one end of the breaking shaft 46 which comprises a portion 46 ’of smaller diameter forming a fusible part of the aforementioned type. This portion 46 ′ extends in a plane P1, radial or transverse with respect to the axis of rotation of the wheel 28, which is distant from a parallel plane P2 passing substantially through the blades 40 of the fan wheel.

The main shaft 44 is centered and guided in rotation by the bearings 48 in the sheath 50 which surrounds part of the section 44 and of the breaking shaft 46 and which is mounted in an orifice 52 in the body 30 of the fan 16.

As explained in the foregoing, this technology is complex and has drawbacks linked to the fact that the safety function is provided on the shaft line 36 by means of the shaft to be broken 46.

The invention provides a solution thanks to a fan breaking wheel which replaces the breaking tree and makes it possible to simplify the line of the fan wheel drive shaft.

Figures 4 and 5 show an embodiment of the invention. These figures show a fan wheel 128 and its drive shaft line which may essentially include a drive shaft 136.

Although the rest of the fan is not described in the following, reference may be made to the characteristics of the fan described in the above and shown in FIGS. 1 to 3 for an example of integration of the wheel 128.

The shaft 136 comprises at least two cylindrical portions of different diameters and which are connected to each other by a cylindrical shoulder 164. The portion of the shaft 136 of smaller diameter is surrounded by the wheel 128 and comprises a external thread at its free end, on which is intended to be screwed a nut 166.

The wheel 128 comprises a hub 138 carrying an annular row of blades 140 at its periphery.

The wheel 128 is mounted on the shaft 136 by means of fusible link means, which comprise two sockets: a first socket 142 known as for fixing and a second socket 143 said to wear.

The first bush 142 extends along the axis A of rotation of the wheel, inside the hub 138. The bush 142 includes a cylindrical portion 142a and a radial portion 142b, that is to say a annular portion extending in a radial plane or perpendicular to the axis A. The sleeve 142 is mounted on the portion of smaller diameter of the shaft 136 so that its cylindrical portion 142a is located on the side of the nut 166. The sleeve 142 is tightened axially against the shoulder 164 by the nut 166, a washer (here radial) 165 being interposed axially between the nut 166 and the sleeve 142 (and more exactly between the nut 166 and the free end of the cylindrical portion of the sleeve 142).

The internal diameter of the bush 142 and the external diameter of the smaller diameter portion of the shaft 136 can be chosen so that the bush is mounted on the shaft with a tight fit radially, i.e. without radial clearance. The axial tightening of the sleeve 142 on the shaft 136 is sufficient to allow the transmission of a torque between the shaft and the sleeve. However, it is possible to complete this coupling with external splines on the smaller diameter portion of the shaft 136 and complementary internal splines in the cylindrical portion 142a of the sleeve 142.

The radial portion 142b of the sleeve 142 comprises an annular row of axial through-holes 142c passing through screw 174 both fusible and for fixing the sleeve 142 to the wheel 128, and therefore from the wheel 128 to the shaft 136 .

The second bushing 143 extends along the axis A of rotation of the wheel, around the bushing 142 and inside the hub 138. The bushing 143 comprises a cylindrical portion 143a and a radial portion 143b. The sleeve 143 is mounted on the sleeve 142 so that its cylindrical portion

143a is located on the side of the nut 166. The portions 143a, 143b of the sleeve 143 are therefore applied respectively radially and axially on the portions 142a, 142b of the sleeve 142.

The radial portion 143b of the bushing 143 comprises an annular row of axial through-holes 143c aligned with the orifices 142c for the passage of the screws 174. The bushing 143, and more particularly its radial portion 143b, is clamped axially against the bushing, and more particularly its radial portion 142b, by the fixing screws 174.

The internal diameter of the portion 143a of the bushing 143 and the external diameter of the portion 142a of the bushing 142 can be chosen so that the bushing 143 is mounted on the bushing 142 with a tight fit radially, i.e. without radial clearance.

The hub 138 of the wheel comprises a cylindrical portion 138a and a radial portion 138b, the cylindrical portion 138a being located on the side of the nut 166.

The wheel 138 is mounted around the bushing 143 so that its portions 138a, 138b are applied respectively radially and axially to the portions 143a, 143b of the bushing 143.

The radial portion 138b of the wheel 138 comprises an annular row of through axial holes 138c aligned with the holes 142c, 143c for the passage of the screws 174. The wheel 138, and more particularly its radial portion 138b, is axially tightened against the bushing 143, and more particularly its radial portion 143b, by the fixing screws 174.

The internal diameter of the portion 138a of the wheel and the external diameter of the portion 143b of the sleeve 143 can be chosen so that the wheel 138 is mounted on the sleeve with a tight fit radially, that is to say without play radial.

As best seen in Figure 5, the free ends of the cylindrical portions 143a, 138a of the sleeve 143 and the hub 138 are separated from an axial clearance J of the washer 165 so that the axial clamping of the hub on the sockets are obtained only by the screws 174 (and not also by the nut 166) and that the wheel 128 is fixed to the shaft 136 only by these screws 174.

In the example shown, the screws 174 have their heads applied against the radial wall 142a of the sleeve 142, and receive a nut tightened against the radial wall 138b of the hub 138. The screws are for example three in number and regularly distributed around of axis A.

Each screw 174 is preferably mounted without radial clearance in the orifices 142c, 143c and 138c. For this, these holes can be made simultaneously by drilling with a drill whose diameter is equal to the diameter of the threaded part of the screw.

These are 174 fuse screws, that is to say they are configured to break, and split into two parts, when they are subjected to a shear above a certain threshold. This shear threshold and the number of screws are determined as a function of a torque threshold transmitted by the shaft beyond which a rupture of the screws is sought. To do this, they may include a zone of weakness and of initiation of rupture, for example in the form of a thinning of section, that is to say a local reduction in diameter.

When the torque transmitted by the shaft 136 is greater than the predetermined threshold, the screws 174 will rupture and cause the wheel 128 to disengage from the shaft 136. The sleeve 142 is held axially tightened by the nut 166 against the shoulder 164 of the shaft 136, and therefore remains integral with the shaft. The shaft 136 can be made to rotate for a certain period of time, for example three hours, while the wheel can remain stationary. During this rotation, the wear sleeve 143 is able to wear out by friction and / or overheating to avoid seizing or welding of the sleeve 142 and the hub 136.

In the event that the sleeve 143 disappears at least in part, and for example after three hours, the wheel would be liable to fall. If the axis A is vertical, the wheel could fall on the body 130 of the fan. If the axis A is horizontal, the wheel could fall on the portion of larger diameter of the horn 129 of the fan body because the radial clearance between the wheel and the horn (for example of the order of 0.3 mm) is preferably less than the radial thickness of the sleeve 143. The shaft 136 could continue to rotate for three hours.

For example, the hub 138 and the blades 140 are made of aluminum and the shaft 138 is made of stainless steel. The socket 142 can be made of metal (for example stainless steel) and the socket is preferably made of plastic material, chosen for example from: PEEK GL30 or PEEK CA30, POM-C, PA66, VESPEL®, ULTEM®, etc. .

In order to guarantee alignment between the wheel 128 and the sockets

142, 143, assembly and fixing by screws 174 can be carried out after a first step of roughing the wheel, and before a step of machining the wheel.

In a variant not shown, the screws 174 could be replaced by rivets, also fusible.

Claims (9)

1. Fan (16), in particular for an aircraft cooling group, comprising: - a wheel (128) comprising a hub (138) and an annular row of blades (140), - a shaft line (136) for driving the wheel around an axis (A), and - Fuse connecting means of the wheel hub to the shaft line, these fuse connecting means comprising a first fixing bushing crossed by the shaft line and surrounded by said hub, and fusible elements (174) of safety devices which extend parallel to said axis (A) and are configured to rupture and disengage in rotation the wheel from the shaft line when a wheel drive torque transmitted by said shaft line exceeds a certain threshold , characterized in that said connecting means comprise a second wear bush (143) which is interposed between said first bush and said hub and which is traversed by said fusible elements, said second bush being made of a material different from that of the first bushing and susceptible to wear by friction and / or by heating in the event that the shaft line continues to rotate following the abovementioned separation e. 2. Fan (16) according to claim 1, wherein said second bushing (143) comprises a cylindrical portion (143a) and a radial portion (143b), the cylindrical portion of the second bushing being interposed between cylindrical portions (142a, 138a) of the first bush (138) and the hub (138), and the radial portion of the second bush being interposed between radial portions (142b, 138b) of the first bush and the hub. 3. Fan (16) according to claim 1 or 2, wherein said fusible elements are screws (174) and ensure the fixing of the wheel (128). 4. Fan (16) according to claim 3, dependent on claim 2, wherein the screws (174) axially pass through the radial portions (142b, 143b, 138b) of the first and second sockets (142, 143) and of the hub (138). 5. Fan (16) according to the preceding claim, in which the screws (174) pass substantially axially through the axial orifices (142c, 143c, 138c) of the radial portions (142b, 143b, 138b) of the first and second sockets (142, 143) and the hub (138). 6. Fan (16) according to one of the preceding claims, wherein said first sleeve (142) is held axially clamped against a shoulder (164) of the shaft line (136) by a nut (166) screwed to a end of the tree line. 7. Fan (16) according to the preceding claim, dependent on claim 5, wherein said nut (166) bears axially on a washer (165) which itself bears axially on the cylindrical portion (142a) of the first sleeve (142), this washer being separated by an axial clearance (J) from the cylindrical portions (143a, 138a) of the second sleeve (143) and of the hub (138). 8. Fan (16) according to one of the preceding claims, wherein said first sleeve (142) is made of metal and said second sleeve (143) is made of plastic. 9. Aircraft cooling group, comprising a heat exchanger, for example air-oil, and a fan (16) according to one of the preceding claims.